Project Summary Correlates of innate and T-cell immunity in seropositive and serodiscordant subjects for Trypanosoma cruzi infection. T-cell function is central to the control of T. cruzi. When immune control is inefficient, parasite load and inflammation, and thus the potential for tissue damage, increase. The observation that subjects with one positive conventional test out of three performed as recommended by WHO for the diagnosis of Chagas disease, regarded as ?serodiscordant subjects?, have more functional T. cruzi-specific T-cell responses, and the responses are of a higher magnitude compared with those of seropositive chronically T. cruzi-infected individuals suggests that some subjects exposed to T. cruzi might actually resolve the infection. The hypothesis to be tested in the proposed study is that serodiscordant subjects who are presumed to have cleared the infection would display not only high functional T-cell responses but also heightened innate immune responses. The study will also explore the extent to which innate immune responses are exhausted during the chronic phase of the infection. Based on extensive preliminary data produced in the applicants? laboratories, these hypotheses will be tested by pursuing three specific aims: 1) determine the levels, phenotype and function of innate immune cells in serodiscordant and seropositive subjects for T. cruzi infection and their association with T-cell responses; 2) determine the levels of T. cruzi-specific memory and antibody-secreting cells and the activation status of total B cells in serodiscordant subjects; and 3) determine the effect of treatment with benznidazole on innate immune responses and the association with changes in T-cell responses. Under Aim 1, the frequencies, phenotype and function of natural killer (NK) cells, innate lymphoid cells (ILCs) and monocyte subsets will be measured in serodiscordant subjects in comparison to chronically T. cruzi-infected subjects with different degrees of cardiac dysfunction. Innate immune profiles in these subjects will be correlated with T. cruzi-specific T-cell responses, extensively characterized by our group. Under Aim 2, we will answer the question of whether the low levels of T. cruzi- specific antibodies in serodiscordant subjects are associated with a skewed presence of memory B cells vs. antigen-driven antibody-secreting cells specific to T. cruzi antigens. The activation status of total B cells will also be determined in serodiscordant subjects and compared with the findings in seropositive subjects. Finally, under Aim 3, we will explore the extent to which treatment with benznidazole in chronically T. cruzi- infected subjects induces changes in innate immune responses and whether successful treatment might be predicted by a combination of changes in innate and adaptive immune parameters. The proposed study is innovative because we postulate that the induction of efficient T-cell and innate immune responses might eventually cure or control T. cruzi infection. Completion of the experiments proposed in this project will provide insights into the meaning of serodiscordance for T. cruzi infection. These contributions will be significant for understanding the relationship between adaptive and innate immune responses in relation to cardiac dysfunction and how these responses are modulated by etiological treatment.